1. Technical Field
The present invention generally relates to the field of video processing, and more particularly to improving the quality of images having blended graphics, such as where logos or text are provided as a region of interest (ROI) of the video.
2. Related Art
Video that once was only watched on living room televisions is now being rescaled and reformatted for consumption on smartphones, tablets, laptops, PCs, etc. There are now many form factors for display devices and more resolutions including adaptive bit rate (ABR) applications and ultra high definition televisions (UHDTV) available.
Broadcast television signals include image frames that can have overlaid graphics elements, such as text, logos, scores for sporting events or other graphics that form the ROIs. Coding and then decoding video for different formats can distort the ROI quality. The readability of ROIs are reduced when video content is rescaled for display on a small screen such a smartphone. Readability is also reduced when content is encoded at less than full resolution, such as commonly the case in ABR and over-the-top (OTT) applications. Current ABR and OTT encoders, transcoders, and stream processors process video in a manner that is sensitive to the overall human visual acuity, not to the text & symbol content in video.
In addition to distortion due to a change in video format, in some circumstances the ROI cannot be effectively separated from the background graphics resulting in distortion of the blended graphics when the video is encoded and decoded. For example, a broadcaster may overlay a company logo in the lower-right corner of program image frames to indicate that the program was received from their transmission facilities. If the ROI in the form of a logo is transparent, it can be difficult to visibly separate the ROI from the background, particularly when the screen size is reduced or altered. The data values can be a combination of text contributions from both the image and an overlaid ROI, making the separate text difficult to separate during video processing. To enable distortion to be reduced for combined images during the encoding and decoding process, accurate identification of the boundaries or edges of the graphics is desirable, particularly where the ROI is transparent or appears blended with the background.
It is desirable to provide techniques to prevent distortion and improve quality of the ROI during video processing, particularly when screen size is significantly reduced relative to what was intended for the original video.